1. Field of the Invention
This invention relates to a method for the preparation of high-melting C.sub.4 -hydrocarbon resins. The resins show units which are chiefly derived from 1,3-butadiene, isobutene, 1-butene, cis-2-butene and trans-2-butene, that is, from olefins of the C.sub.4 -hydrocarbons.
2. Description of the Prior Art
In the presence of cationic, anionic or radical catalysts and also in the absence of catalysts, it is possible to polymerize the aforementioned C.sub.4 -hydrocarbons in known fashion, singly and also in the presence of various additives. For example, butadiene typically yields, depending on the nature of the catalysts and of the reaction conditions, gummy materials and cyclic oligomers. In the presence of AlCl.sub.3 as a catalyst, butadiene yields a sticky, amorphous material which is clearly not technically satisfactory as an elastomer. Isobutene and 1-butene yield sticky elastomers and polymers, but no high-melting resins. Trials to polymerize 2-butene, did not yield typical resins either, but mostly gave rise to oily products of low molecular weights.
The polymerization of single olefins of C.sub.4 -hydrocarbons to resins is obviously unsatisfactory or does not occurr at all. It should be mentioned that mixtures of C.sub.4 -olefins can occurr in the following compositional ranges as the so called C.sub.4 -cuts during the cracking of petroleum to ethylene and propylene:
______________________________________ butadiene 30-50% isobutene 20-35% 1-butene 10-20% 2-cis/trans-butene 5-20% n-butane 2-10% isobutane 1-3% other C.sub.3--5 -hydrocarbons less than 2% ______________________________________
Experiments were thus undertaken, wherein mixtures of C.sub.4 -olefins, especially those which contained butadiene and isobutene, were polymerized with various catalysts. It was thus found, in accordance with the hereinafter described references that butadiene-free C.sub.4 -olefins only yield oily polymerizates, wherein with increasing butadiene content, the polymerization gives rise predominantly to elastic products. The cationic polymerization of mixtures of butadiene-containing C.sub.4 -olefins with aluminum halides gives rise according to DT-OS No. 2053788 to resins. Although these resins are solids at room temperatures, they are technically not very satisfactory; only through the addition of C.sub.5 -olefins to the polymerization was it possible to improve the results. It is known, according to JA-ASS Sho No. 43-38813 and Sho 45-15435 to prepare somewhat higher melting resins from butadiene-containing C.sub.4 -cuts even at low temperatures and in the presence of C.sub.5 -olefins or with concomitant aging. The latter is disadvantageous in that the resins become darkened.
It has been discovered that, surprisingly, butadiene-rich C.sub.4 -olefins can be transformed to high-melting resins with the aid of protonated aluminum halide-catalysts (Friedel-Crafts catalysts), when the polymerization occurs at temperatures starting at 30.degree. C. and the butadiene content is preferably at least 50%. Further surprising is that the formation of polymerizates with superior elastic properties is excluded.